The present invention generally relates to railroad cars and, more particularly, to a method of manufacturing an energy absorption apparatus for a railroad car.
Impact forces of significant magnitude are commonly imparted to railroad cars during their use. For example, draft gears are provided toward opposite ends of each railroad car to absorb axially directed impact forces applied to the railroad car when the cars are operably coupled to each other and during transportation of the railroad car between locations. Side bearings are also commonly used on railroad cars to control or impede xe2x80x9chuntingxe2x80x9d movements of wheeled trucks on the railroad car and to control rolling movements of the railroad car body about a generally horizontal axis. Typically, a side bearing is disposed on opposite lateral sides of a longitudinal axis of the car between a bolster of a wheeled truck and the body of the railroad car. While the present invention is disclosed and described for use with a railroad car side bearing, it should be appreciated that the principals and application of the present invention extend beyond railroad car side bearings to additional or other forms of energy absorption assemblies for railroad cars.
Hunting is a phenomenon created by the wheeled trucks during movement of the railroad car over tracks. The coned wheels of each truck travel a sinuous path along a tangent or straight track as they continually seek a centered position under the steering influence of wheel conicity. In traveling such a sinuous path, a truck will yaw cyclically with respect to the car body about a vertical axis defined by the vertical centerline of the truck bolster. Of course, the truck also yaws or rotates quasi-statically with respect to the car body in negotiating curved track. As a result of the afore-mentioned cyclic yawing, xe2x80x9chuntingxe2x80x9d can occur as the yawing becomes unstable due to lateral resonance that can develop between the car body and the truck. As will be appreciated by those skilled in the art, excessivexe2x80x9chuntingxe2x80x9d can result in premature wear of the wheeled truck components including the wheels, bolsters, and related equipment. Hunting can furthermore cause damage to the lading being transported in the car body of the railroad car.
Typically, a side bearing includes a base housing or cage which mounts to the bolster of the wheeled truck, a top plate, and a spring disposed between the top plate and base. In one form, the top plate and base are arranged in telescopic relation relative to each other. The spring of each side bearing places a predetermined preload on the top plate. When assembled on the railroad car, this vertical force or preload developed by the spring acts essentially to keep the top plate of the side bearing in constant contact with the underside of the body of the railroad car to impede yaw axis motion of the truck. Thus, these types of side bearings are sometimes referred to as xe2x80x9cconstant contactxe2x80x9d side bearings. For purposes of this description, however, the term xe2x80x9cside bearingxe2x80x9d will be used throughout. As the truck yaws, the top plate of the side bearing slides across an underside of the car body. The resulting friction forces produce an opposite torque which acts to inhibit yaw motion. The preload or vertically directed force placed on the top plate of each side bearing by the spring furthermore serves to limit the roll motion of the car body.
Especially in connection with railroad car side bearings, it should be noted that while a sufficient preload or vertically directed force needs to be maintained against the underside of the truck body to impede truck hunting, there is a limit to the maximum vertically directed force or preload which can be effectively applied against the underside of the truck body. According to AAR Specifications for Design and Fabrication of Freight Cars, and in order for the wheeled truck to turn, thus allowing the railroad car to negotiate curves, the preload developed by the side bearing spring is limited to 85% of the weight of the railroad car body. Furthermore, during assembly of a new railroad car or when existing railroad cars are retrofitted with new side bearings, the vertically directed force developed by the spring of the side bearing must allow a centerplate on the body of the railroad car to operably engage the truck bolster after a relatively short time period, ie., 24 hours, thereby enabling the railroad car to be released for service.
Recently, different forms of elastomeric materials have been used as the spring for such railroad car side bearings. One such spring is marketed and sold by the Assignee of the present invention under the tradename TecsPak. This form of resilient spring is formed from a HYTREL elastomer, manufactured and sold by the DuPont Company. Ordinarily, a HYTREL elastomer has inherent physical properties that make it unsuitable for use as a spring. Applicant""s assignee, however, has advantageously discovered methods by which the copolyesther polymer elastomer sold under the name HYTREL can be converted into a compression spring material. Generally, this method involves the application of a one-time compressive force to a body of HYTREL material so as to compress the body in an axial direction to an extent greater than 30% of its initial axial length.
Heretofore, after an elastomeric spring is formed, it is assembled into the side bearing and, ultimately, used in service on the railroad car. Research reveals, however, side bearings using elastomeric springs experience a significant reduction in the preload force applied by the spring after only a limited time in service. Of course, a reduction in the preload or force developed by the spring correspondingly effects the engagement force between the top plate of the side bearing and the underside of the railroad car body thereby limiting the ability of the side bearing to impede the yaw axis rotation or hunting of the wheeled truck as the car moves along the track which can result in premature wear of the truck components including the wheels, bolster and related parts and equipment. Applicants research has further revealed that after this limited time of in-service use of the side bearing has expired, any further reduction in the preload developed by the side bearing against the underside of the railroad car body takes place at a considerably slower rate.
Thus, there is a need and a desire for a process for manufacturing an energy absorption apparatus for a railroad car which utilizes an elastomeric spring and wherein a substantially constant preload or force is maintained by the energy absorption apparatus during and continuing after initial use of the energy absorption apparatus on the railroad car.
In view of the above, and in accordance with the present invention, there is provided a process or method of manufacturing an energy absorption apparatus for a railroad car. The energy absorption apparatus of the present invention offers enhanced performance characteristics by minimizing the initial reduction in preload force developed for the energy absorption apparatus. Broadly stated, the method or process of the present invention comprises the steps of: providing an elastomeric spring member having an initial shape including an initial height between opposed ends thereof; and stabilizing the elastomeric spring member prior to its insertion between first and second members of the energy absorption apparatus. Stabilization of the elastomeric spring through a manufacturing process and prior to insertion of the energy absorption apparatus into operable combination with the railroad car maximizes and maintains a substantially constant elastomeric spring preload while simulating a predetermined wear condition for the energy absorption apparatus.
An important feature of the present invention relates to the process or method for stabilizing the elastomeric spring prior to the energy absorption apparatus being arranged in operative combination with the railroad car. A salient feature of such process involves creating a predetermined wear condition in the elastomeric spring for the railroad car apparatus prior to insertion of said apparatus into operable combination with the rail car. In one form, creating a predetermined wear condition in the elastomeric spring is effected by conditioning the elastomeric spring to exert a substantially stabilized preload force between members of the railroad car apparatus before the railroad car apparatus is inserted into operable combination with the rail road car. According to one form, conditioning the spring to exert a substantially stabilized preload force is effected as a result of cyclically compressing the elastomeric spring in a predetermined repeat pattern prior to insertion of the spring into operative combination with the energy absorption apparatus. Applicant""s testing and analysis has surprisingly revealed the repeated cyclical compression of the elastomeric member forming the spring effects permanent deformation of the elastomeric member while simultaneously reducing the initial preload to an acceptable level, thus, simulating a predetermined wear condition for the energy absorption apparatus and thereby minimizing the reduction in preload force developed by the energy absorption apparatus when initially installed on the railroad car.
According to a preferred process or method of forming or manufacturing the elastomeric spring, each individual compression cycle for the elastomeric member of the energy absorption apparatus includes the steps of: compressing the elastomeric member to a predetermined height; holding the compressed elastomeric member at the compressed height for a predetermined time period; and releasing the compressed elastomeric member. When the elastomeric spring member is formed from a HYTREL material, each individual compression cycle for the elastomeric spring comprises the steps of: compressing the elastomeric spring member beyond the plastic limit thereof; holding the compressed elastomeric member for a predetermined time period; and, releasing the compressed elastomeric spring member.
The methodology of the present invention furthermore preferably includes the steps of repeating the individual compression cycles for the elastomeric member of the energy absorption apparatus a predetermined number of times. Testing has revealed the compression cycles will vary depending upon the type of elastomer used for the spring. With the elastomeric material having an elastic to plastic strain ratio greater than 1.5 to 1, the predetermined repeat pattern for the elastomeric member can vary between about 5 and about 100 individual compression cycles. The most preferred method of forming the elastomeric spring involves compressing the elastomeric spring in a repeated pattern comprised of about 10 individual compression cycles.
The methodology of the present invention can be furthermore enhanced through use of a press for compressing the elastomeric spring members. Moreover, several elastomeric members are preferably arranged in the press at the same time such that several elastomeric springs are conjointly formed relative to each other at the same time.
According to another form of the invention, the process or method of enhancing spring performance is directed to side bearings for railroad cars. According to this form of the invention, the process or method comprises the steps of: providing a top plate; providing a base arranged in axially spaced relation relative to the top plate; and, inserting an elastomeric spring member formed according to the principals of the present invention between the top plate and the base.
When used in side bearings, the elastomeric spring member preferably has an elongated and generally cylindrical configuration between opposed ends thereof. The elastomeric member forming the spring can further include a centralized opening extending therethrough and opening at opposite ends thereof. Applicant has found that forming the spring member from an elastomeric material having an elastic to plastic strain ratio greater than 1.5 to 1 offers beneficial results over other elastomeric materials.
According to still another form, there is provided a method for manufacturing a side load bearing which is insertable between a bolster of a wheeled truck and a railroad car body to impede hunting movements of the wheeled truck. In this form, each side load bearing includes an elastomeric spring accommodated between a base and a top plate. The method comprises the step of creating a predetermined wear condition in the elastomeric spring for the side load bearing. Creation of a predetermined wear condition in the elastomeric spring of the side load bearing can be accomplished by conditioning the elastomeric spring of the side load bearing such that a substantially stabilized preload force is placed upon the top plate by the spring before the side load bearing is installed or inserted between the bolster on the wheeled truck and the railroad car body.
It is, therefore, a primary object of the present invention to present a method of manufacturing an energy absorption apparatus including a specifically formed elastomeric spring housed between the housing members of a railroad car energy absorption apparatus to provide a maximum level of performance for the energy absorption apparatus.
Another object of the present invention is to present a method of manufacturing a railroad car side bearing including an elastomeric spring housed between a base and a top plate and wherein the side bearing is adapted for insertion between a bolster of a wheeled truck and a railroad car body to offer surprising enhanced performance in impeding hunting of the wheeled truck.
The elastomeric spring is conditioned or treated in such a manner such that a substantially constant and stabilized spring force is produced by the energy absorption apparatus. When the principals of the present invention are applied to a railroad car side bearing, stabilization of the preload force developed by the conditioned elastomeric spring simulates a predetermined wear condition for the side bearing. Thus, the side bearing with the treated elastomeric spring provides near optimal control of xe2x80x9chuntingxe2x80x9d responses of the wheeled truck, even during the initial period of use, thus yielding significant advantages to the end user.
Another object of the present invention is to provide a method whereby the performance of a railroad car energy absorption apparatus is significantly enhanced, especially during initial use, without increasing parts, or substantially increasing the cost of the energy absorption apparatus.
Still another object of the present invention is to provide a railroad car side bearing having significantly enhanced performance characteristics, especially during initial use of the side bearing, through relatively simple changes in the process of manufacturing the elastomeric spring forming part of the side bearing.
These and other objects, aims and advantages of the present invention are more fully described in the following detailed description, the appended claims, and drawings.